Owing to the discontinuous method of operation, a number of different vibration phenomena occur in an internal combustion piston engine. Torsional vibrations in the drive train of a vehicle caused by torque fluctuations of the internal combustion engine are particularly noticeable. These vibrations propagate over the other vehicle components and often lead to a noise and vibration level that disturb the vehicle occupants. The linear vibrations of the entire engine block caused by inertial forces associated with the internal combustion engine, which can also propagate over the drive train, are also significant.
To reduce these torsional vibrations, DE 41 00 937 A1 proposes that a passive torsional vibration dampener be arranged in the drive train of the vehicle between its internal combustion engine and its transmission. The proposed passive dampener has an input part driven by the internal combustion engine and an output part positioned on the input shaft of the transmission. The output part is connected to the input part in torsionally elastic fashion by a spring system. An active torsional vibration dampener in the form of an electric machine is also provided in the drive train behind the previously mentioned passive torsional vibration dampener. The rotor of the active torsional vibration dampener sits on the input shaft of the transmission and counteracts the torque fluctuations still remaining at the output of the passive torsional vibration damper. However, this arrangement is often unusable under practical conditions because of the limited space available in the drive area of many vehicles.
A starter/generator whose rotor sits on a rotating shaft with a drive unit, (for example, a crankshaft of an internal combustion engine), and at the same time is designed as a passive torsional vibration absorber, is also known from DE 44 06 481. The rotor of this known apparatus consists of a ring-like absorption mass (elastically connected via a rubber layer), which can be rotated relative to the rotating shaft within the scope of elastic couplings. The elastic couplings do not interrupt the torque path of the shaft. Instead, the shaft is rigidly continuous. Thus, instead of performing vibration dampening, the elastic couplings serve only for coupling a free absorber mass to the shaft.
The absorber effect of this known apparatus is achieved by detuning the oscillation system. Specifically, by virtue of the absorber mass, the base system acquires an additional degree of freedom which shifts the resonance frequencies. This expedient, however, is only fully effective if excitation of the base system occurs with a fixed frequency in the vicinity of (unshifted) resonance. Since internal combustion engines are generally operated with variable speed, and since the number of vibration absorbers that can be implemented under practical conditions is limited, resonances are unavoidable under this known approach.